1. Field of the Invention
Embodiments of the invention relate to methods for addressing messages in a computer network.
2. Background of the Related Art
With increasing numbers of participants on computer networks, the address types in such computer networks can reach capacity limits, making it necessary to convert to different address types. An example of this is the conversion of addressing on the Internet from IPv4 addressing to IPv6 addressing. Almost immediately, more and more (sub-)networks are having to be converted to IPv6 addressing, because the latest estimates are that already next year there will be no more new IPv4 addresses available.
On the other hand, however, both IPv4 and IPv6 addresses and corresponding sub-networks will still coexist for many years. Given the large number of existing installations, it will be several years, possibly ten or even twenty years, before the last IPv4 network elements are switched off. During this switchover period, both address types will have to be used together. For some services, such as voice and video (VVoIP) services based on the Session Initiation Protocol, there are already converters between the two address types, which are often in the form of a Session Border Controller (SBC) with an integrated Media Gateway (MGW).
IPv4 offers addressing space for a little over four billion IP addresses (232=4,294,967,296) for addressing computers and other devices. In the early stages of the Internet, when there were only a few computers that needed an IP address, this was more than sufficient. Due to the unforeseen growth of the Internet, however, today there is a shortage of addresses. On Feb. 1, 2011, IANA allocated the last two unreserved networks to the Asian Regional Internet Registry APNIC; according to an agreement from 2009, the remaining address space was distributed equally to the regional address assignment authorities on Feb. 3, 2011. Beyond that, the regional address assignment authorities no longer have any IPv4 address space available to them. A prognosis from the chief scientists at APNIC, which is updated daily, shows that the first Regional Internet Registry, APNIC, will have no more addresses available for the Internet community as of July 2011.
The historic development of the Internet poses another problem: due to the fact that the practice of assigning IPv4 address space changed several times over time, it became highly fragmented, so that often a number of non-related address ranges belong to the same organization. Combined with the routing strategy used today (Classless Inter-Domain Routing), this leads to long routing tables, to which storage devices and processors for routers in the core area of the Internet must be configured. Furthermore, IPv4 requires routers to re-calculate checksums for each forwarded packet, adding to the processor load.
For these reasons, the IETF started work on IPv6 in 1995. In December 1998, with the publication of RFC 2460 in the Standards Track, IPv6 was officially named as the successor to IPv4.
The significant new features of IPv6 include:                a) An increase in address space from IPv4 with 232 (˜4.3 billion=4.3·109) addresses to 2128 (˜340 undecillion=3.4·1038) addresses with IPv6, i.e. increased by a factor of 296         b) Simplification and improvement of the protocol structure (header data); this is especially important for routers.        c) Automatic classless configuration of IPv6 addresses; classful processes like DHCP are therefore unnecessary when using IPv6 in many application situations        d) Mobile IP as well as simplified renumbering and multi-homing        e) Implementation of IPsec within the IPv6 standard. This makes it possible to encrypt IP packets and check them for authenticity. For IPv4, IPsec support is only optional.        f) Support of network techniques such as Quality of Service and Multicast.        
The primary motivation for increasing address space lies in preserving the end-to-end principle, which is a central design principle of the Internet: Only the end nodes of the network should conduct active protocol operations, and the network between the end nodes is only responsible for forwarding data packets. (In this regard, the Internet differs significantly from other digital data transfer networks such as GSM.) This makes it necessary for every network node to be addressable in a globally unique manner.
Today's commonly used methods such as Network Address Translation (NAT), which at present bypass the IPv4 address shortage, violate the end-to-end principle. They make it possible for connected computers to generate only outgoing connections, so they cannot be contacted readily from the Internet. Also IPsec or higher-layer protocols like FTP and SIP rely in part on the end-to-end principle and have only limited functionality with NAT or require additional solutions. Especially for home users, IPv6 implies a paradigm shift: Instead of being assigned just one IP address from the provider and having to link multiple devices to the Internet through NAT, the user receives a globally unique IP address space available for an entire sub-network, so that each of his devices can have an IP address on that sub-network. This makes it easier for end users to participate actively on the network by offering services, and it eliminates the problems resulting from NAT address transcription.